Objective: Although protruding ears are one of the most frequently occurring congenital deformities in the craniofacial area, there is no clear consensus in literature as to the definition. Our aim was to provide a clear delineation for the definition of prominent ears, deduced from the anthropometry of normal (nonprotruding) ears. Methods: We performed a prospective cohort study to assess the anatomy of the normal auricle in children using computer-assisted anthropometry in photographs of 102 children aged 5 to 18 years. We compared the anatomy to retrospectively assess photographs of 44 patients who were listed for prominent ear correction. Results: Our results show that protrusion differs statistically between sexes. In view of these data, an ear could be defined as prominent when the upper protrusion exceeds 21.5 mm or the lower protrusion exceeds 20.0 mm in boys and the upper protrusion exceeds 17.5 mm or the lower protrusion exceeds 15.5 mm in girls. Using these demarcations, 87.5% of our operated prominent ears would qualify as a prominent ear. In addition, we found that prominent ears have larger auricular lengths and consequently larger surface measurements compared with normal ears (P = 0.001). Up to 19.3% of the normal ears showed an asymmetry of more than 3 mm concerning protrusion. Conclusions: Protrusion differs significantly between sexes. This indicates that different criteria should be used to judge protrusion in boys and girls. None of our prominent ears exceeded only the demarcation in the lower protrusion, suggesting that upper protrusion plays a larger role in the perception of prominence than lower protrusion and should therefore be the main objective of corrective otoplasty. Furthermore, the variation of asymmetry of protrusion in the normal population indicates that an often used success criteria in otoplasty of an asymmetry less than 3 mm may be too strict.